1. Field of the Invention
This invention relates to a testing contactor for semiconductor devices, specifically power devices.
2. Discussion of the Related Art
Semiconductor devices comprise a more or less oblate parallelepipedic body having electrical connection leads. It is common practice to test such devices, prior to shipment, one at a time to check performance specifications. To this end, their leads are connected electrically to an automatic test apparatus which applies predetermined test currents across lead pairs, and measures the voltage drop across the two leads inside the device. Similar tests are performed manually on individual semiconductor devices for design verification, specific sampled quality checks, or other purposes.
Usually, the test current is supplied with the intermediary of a contactor which carries plural electric contact elements spring loaded toward the leads. The voltage drop is measured across these contact elements.
Power devices may require relatively large currents (on the order of some amperes), so the contact resistance between the leads and electric contact elements becomes significant. For this reason, measuring the voltage drop across the electric contact elements, rather than across the lead, produces a measured voltage value made greater by the voltage drop across the two contact resistances. This would distort the test measurements to a largely unforeseeable extent, since contact resistance varies with such uncontrolled factors as pressure, actual contact area, surface finish, ambient temperature, cleanliness, etc.
To eliminate such errors, so-called Kelvin contacts are used. Kelvin contacts are in practice dual contacts placed side-by-side; one contact element (the "forcing" contact) is used to supply current, and the other contact element (the "sensing" contact) is used to transmit the resulting voltage drop and is connected to a voltage meter. The voltage drop due to contact resistance of sensing contacts is negligible because the current flowing through the sensing contacts is very small. However, there are semiconductor devices, including semiconductor power devices that are so small that the Kelvin contacts cannot be used with the contact elements laid side-by-side. It would be possible to press the two contact elements against the lead from opposite sides but this solution is unacceptable because it makes for significantly different pathlengths of the sensing and forcing wires which, in tests conducted at high frequencies, introduces errors.
One object of the invention is to provide a testing contactor which uses Kelvin contacts and which can be used with small-size semiconductor devices, i.e., devices whose leads are less than 5 mm long, less than 1 mm wide, and are spaced less than 2 mm apart.